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Nonsense mutation
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== Simple example == [[DNA]]: 5β²βATG ACT CAC <span style="background-color:#ccf">CGA</span> GCG CGA AGC TGAβ3β² 3β²βTAC TGA GTG <span style="background-color:#ccf">GCT</span> CGC GCT TCG ACTβ5β²<br> [[mRNA]]: 5β²βAUG ACU CAC <span style="background-color:#fcc">CGA</span> GCG CGA AGC UGAβ3β²<br> Protein: Nβ[[methionine|Met]] [[Threonine|Thr]] [[Histidine|His]] <span style="background-color:#ffc">[[Arginine|Arg]]</span> [[Alanine|Ala]] [[Arginine|Arg]] [[Serine|Ser]] [[Stop codon|Stop]]βC The example above begins with a 5' [[DNA sequence]] with 24 [[nucleotide]]s (8 triplet codons) seen and its complementary strand shown below. The next row highlights the 5' [[Messenger RNA|mRNA]] strand, which is generated through [[Transcription (biology)|transcription]]. Lastly, the final row showcases which the [[amino acid]]s that are [[Translation|translated]] from each respective [[codon]], with the eighth and final codon representing the [[stop codon]]. The codons corresponding to the fourth amino acid, [[Arginine]] (Arg), are highlighted because they will undergo a nonsense mutation in the following figure of this example. [[DNA]]: 5β²βATG ACT CAC <span style="background-color:#8888ff">T</span><span style="background-color:#ccf">GA</span> GCG CGA AGC TGAβ3β² 3β²βTAC TGA GTG <span style="background-color:#8888ff">A</span><span style="background-color:#ccf">CT</span> CGC GCT TCG ACTβ5β²<br> [[mRNA]]: 5β²βAUG ACU CAC <span style="background-color:#ff8888">U</span><span style="background-color:#fcc">GA</span> GCG CGU AGC UGAβ3β²<br> Protein: Nβ[[methionine|Met]] [[Threonine|Thr]] [[Histidine|His]] <span style="background-color:#ffff88">[[Stop codon|Stop]]</span>βC Now, suppose that a nonsense mutation was introduced at the fourth codon in the 5β² DNA sequence (CGA) causing the [[cytosine]] to be replaced with [[thymine]], yielding TGA in the 5β² DNA sequence and ACT in the complementary strand. Because ACT is transcribed as UGA, it is translated as a stop codon. This leads the remaining codons of the mRNA to not be translated into protein because the stop codon is prematurely reached during translation. This can yield a truncated (''i.e.'', abbreviated) protein product, which quite often lacks the functionality of the normal, non-mutant protein.<ref name=":1" /> {| align="center" class="wikitable" style="border:none;" |+ All possible nonsense mutations ! scope="col" | ''amber'' ({{mono|UAG}}) mutations ! scope="col" | ''ochre'' ({{mono|UAA}}) mutations ! scope="col" | ''opal'' ({{mono|UGA}}) mutations |- | <span style="font-family: monospace"><span style="background-color:#ff8888">A</span>AG (Lys)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>AG (stop)</span><br> <span style="font-family: monospace"><span style="background-color:#ff8888">C</span>AG (Gln)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>AG (stop)</span><br> <span style="font-family: monospace"><span style="background-color:#ff8888">G</span>AG (Glu)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>AG (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">C</span>G (Ser)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">A</span>G (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">G</span>G (Trp)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">A</span>G (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">U</span>G (Leu)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">A</span>G (stop)</span><br> <span style="font-family: monospace">UA<span style="background-color:#ff8888">C</span> (Tyr)</span> β <span style="font-family: monospace">UA<span style="background-color:#ff8888">G</span> (stop)</span><br> <span style="font-family: monospace">UA<span style="background-color:#ff8888">U</span> (Tyr)</span> β <span style="font-family: monospace">UA<span style="background-color:#ff8888">G</span> (stop)</span> | <span style="font-family: monospace"><span style="background-color:#ff8888">A</span>AA (Lys)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>AA (stop)</span><br> <span style="font-family: monospace"><span style="background-color:#ff8888">C</span>AA (Gln)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>AA (stop)</span><br> <span style="font-family: monospace"><span style="background-color:#ff8888">G</span>AA (Glu)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>AA (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">C</span>A (Ser)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">A</span>A (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">U</span>A (Leu)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">A</span>A (stop)</span><br> <span style="font-family: monospace">UA<span style="background-color:#ff8888">C</span> (Tyr)</span> β <span style="font-family: monospace">UA<span style="background-color:#ff8888">A</span> (stop)</span><br> <span style="font-family: monospace">UA<span style="background-color:#ff8888">U</span> (Tyr)</span> β <span style="font-family: monospace">UA<span style="background-color:#ff8888">A</span> (stop)</span><br> {{mono| }} | <span style="font-family: monospace"><span style="background-color:#ff8888">A</span>GA (Arg)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>GA (stop)</span><br> <span style="font-family: monospace"><span style="background-color:#ff8888">C</span>GA (Arg)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>GA (stop)</span><br> <span style="font-family: monospace"><span style="background-color:#ff8888">G</span>GA (Gly)</span> β <span style="font-family: monospace"><span style="background-color:#ff8888">U</span>GA (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">C</span>A (Ser)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">G</span>A (stop)</span><br> <span style="font-family: monospace">U<span style="background-color:#ff8888">U</span>A (Leu)</span> β <span style="font-family: monospace">U<span style="background-color:#ff8888">G</span>A (stop)</span><br> <span style="font-family: monospace">UG<span style="background-color:#ff8888">C</span> (Cys)</span> β <span style="font-family: monospace">UG<span style="background-color:#ff8888">A</span> (stop)</span><br> <span style="font-family: monospace">UG<span style="background-color:#ff8888">G</span> (Trp)</span> β <span style="font-family: monospace">UG<span style="background-color:#ff8888">A</span> (stop)</span><br> <span style="font-family: monospace">UG<span style="background-color:#ff8888">U</span> (Cys)</span> β <span style="font-family: monospace">UG<span style="background-color:#ff8888">A</span> (stop)</span> |}
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